Recently, a molded foam is demanded widely as an automobile weather strip and a buffering material against a vibration or a noise generated from a domestic electric appliance or an information device. One desired particularly is a thermoplastic elastomer composition capable of being molded conveniently into a foam. Such thermoplastic elastomer may for example be a dynamically crosslinked thermoplastic elastomer. Such elastomer (disclosed for example in Publication of Unexamined Patent Application No. Hei 6-73222) provides a foam which is more flexible when compared with those of a prior art.
But, a crosslinked rubber component contained in such elastomer can not uniformly be foamed. Namely, an uniform foaming is effected only in a part of a crystalline polyolefin, with the result that the crosslinked rubber component forms a rough cell structure. In addition, a gas escapes from the surface of a foam, resulting in a difficulty in maintaining the outer surface smooth, which leads to a poor appearance. Moreover, such elastomer can not prevent an odor or a discoloration sufficiently, and involves many problems to be solved such as a complicated manufacturing process, a high price of an applicable crosslinking agent and a limited utility due to the contamination resulting from a crosslinking agent and the like employed. On the other hand, an olefinic non-crosslinked thermoplastic elastomer can be foamed uniformly by melting, but a resultant foam involves a problematically high compression set due to an absence of the crosslinking.
The present invention solves the problems described above and is intended to provide a thermoplastic elastomer which can be foamed uniformly throughout the entire composition and which has a low compression set. In addition, the present invention is also intended to provide a foam which is obtained from a thermoplastic elastomer composition described above and which has a low compression set, a highly closed cell, a uniform cell shape, no risk of a contamination with a crosslinking agent due to no use of such crosslinking agent, a high flexibility and an excellent appearance and a process for producing such foam.